2.1 Algorithms

2.1 Algorithms

1. Computational Thinking

   • Allows us to take a complex problem, understand what the problem is, and then develop possible solutions
   • The use of a computer to solve problems
   • 4 Key Areas:
     • Decomposition
       • Breaking down a complex problem or system into smaller, more manageable parts
     • Abstraction
       • Gets rid of the irrelevant stuff in the program
       • Allows to only focus on the important information
     • Pattern Recognition
       • Looking for similarities among and within problems
     • Algorithms
       • Developing a step-by-step solution to solve the problem
       • Algorithms must be detailed & easy to understand so it can be passed onto someone else and have them code it

2. Binary Search

   • List must be in order
   • Middle Value is taken
     • Search is stopped if it is the value is the one you're looking for
     • If middle value is larger than the desired one: Take the values to the left of the middle value
       • Then repeat with the new list
     • If middle value is smaller than the desired one: Take the values to the right of the middle value

3. LInear Search

   • List does not have to be in order
   • First value of list is checked
     • Search is stopped if it is the value is the one you're looking for
     • If not desired value: Check next value on the list
       • Process is repeated until desired value is attained

4. Bubble Sort

   • A method for sorting out unordered lists
   • Take the first and second elements from the list and compare them
     • If element 1 > element 2: Swap
       • Else: Leave it
         • Move along to the next pair of elements (element 2 & 3) and repeat
           • Repeat until you have moved through the whole list and not made any changes
   • Worst case scenario: n*n (n = number of elements) Average number of swaps: n^2

5. Merge Sort

   • A list is split into individual lists, these are then combined (2 lists at a time)
   • Split all elements into individual lists
     • Compare the first element into first two lists
       • Put the smallest at the start of a new list
         • Compare the next element of the 1st list with the next element of the 2nd list
           • Put the smallest into a new list
             • Repeat until first two lists merged
               • Then repeat with other lists
           • If you have two values the same, add one (it doesn't matter from which list), and then add the second

6. Insertion Sort

   • Comparing unsorted elements in an individual list and sorting then out in order
     • In a list, the starting element is a 'sorted' list
       • The rest of the elements are an 'unsorted' list
         • Compare the first element in the 'unsorted' list with all the elements in the 'sorted' list
           • If the current unsorted element is smaller than the interacted sorted element, put it in front of that element (move the other sorted elements along)
           • If the unsorted element is larger, compare it with the next
           • If there are no more elements in the 'sorted' list, put it in the final position
             • Repeat until all elements in the 'unsorted' list are in the 'sorted' list

7. Flow Chart

   • Can be used to represent an algorithm
   • It shows the data that is inputted and outputted
     • It shows the processes (actions) that take place
       • It shows the decisions and repetitions that take place
         • Lines are used to show the flow of control
           • Set shapes are used to represent different functions
             • Diamond - Decision
             • Oval - Start/End
             • Rectangle - Process
             • Parallelogram - Input/Output
             • Rectangle with 2 interior lines - Sub-Process

8. Pseudocode

   • 'Fake code'
   • Part way between English sentences, and programming code
   • It is language neutral (it can be read by programmers who are able to use any language)
   • Dry Run - Walking through an algorithm which sample data, running each step manually
   • Trace Table - A table that follows the values of variables to check for accuracy